Photocatalytic materials exhibit an activity of oxidizing and decomposing not only organic substances but also some of inorganic substances such as nitrogen oxides by utilizing a light that is available at low costs and has a very small burden on environments, as an energy source thereof. With the recent tendency that the photocatalytic materials are used in more extensive application fields such as environmental purification, deodorization, anti-fouling and sterilization, a variety of photocatalytic materials have been developed and researched. In particular, there is a demand for photocatalytic materials capable of exhibiting their activity under irradiation of a visible light, and various researches and developments therefor have now proceeded.
In recent years, it has now been attempted to develop visible light-responsive photocatalytic materials containing tungsten oxide as a base component. However, owing to a poor alkali resistance of tungsten oxide, there is a further demand for titanium oxide-based materials having a higher flexibility.
Many researches have been hitherto made to impart a good visible light responsibility to titanium oxide by adding a metal ion component thereto. For example, Patent Document 1 discloses a visible light-responsive photocatalytic material which is obtained by allowing a transition metal component to coexist when subjecting titanium sulfate or titanium oxysulfate to hydrolysis to synthesize titanium oxide. However, in Patent Document 1, among many transition metal components exemplified in its specification, only Fe was practically used in Examples embodying the invention of Patent Document 1, and the effects of the other transition metal components are not described therein, and are therefore uncertain.
Patent Document 2 discloses a W-containing titanium oxide having a visible light responsive characteristic. However, as far as the Examples described in Patent Document 2 are concerned, the titanium oxides obtained therein have a low crystallinity and the effects of addition of W are uncertain. In addition, in Patent Document 2, only in view of the results of the ammonia elimination experiment, it is described that the W-containing titanium oxide has an activity for decomposing organic substances. However, the ground therefor is unclear and unsatisfactory to attain such a conclusion. Further, in the Examples of Patent Document 2, a fluorescent lamp which emits a light including an ultraviolet light component was used as a light source. Therefore, only from the results of the Examples of Patent Document 2, it is not possible to confirm whether or not the photocatalyst obtained therein have an activity of decomposing organic substances under irradiation of a visible light.